The present invention relates to a method and apparatus for performing knee surgery and more specifically to preparation of one or both condyles of a knee to receive a component of a knee prosthesis.
Unicompartmental Knee Arthroplasty (UKA) and Dual-Compartment Arthroplasty (DKA) have evolved into an effective alternative to Total Knee Arthroplasty (TKA) for the treatment of limited osteoarthritis of the knee. In performing UKA, DKA and TKA, it is necessary to precisely cut the condyles of the femur at the tibial femoral joint in order to obtain a satisfactory fit of the femoral component to the distal end of the femur and maintain soft tissue balance and alignment.
In UKA, DKA and TKA, it is important that the condyles (condyle in the case of UKA) be cut such that the distal surface facing the tibia is perpendicular to the mechanical axis of the patient""s femur. A common procedure in TKA involves drilling a hole in the intramedullary canal several inches along the anatomical axis of the femur starting slightly anterior to the intercondylar notch. The anatomical axis extending from the sulcus at the center of the femur between the condyles to the center of the femoral trochanter is at a slight angle, usually 5 to 6 degrees, to the mechanical axis which extends from the center of the femoral head through the sulcus to the center of the ankle. Following drilling, an alignment rod is positioned in the hole along the intramedullary canal and extends outwardly therefrom. An alignment guide used in combination with the alignment rod directs the cutting instrument along the proper path, anterior to posterior, of the condyles to be cut.
Although drilling a hole in the intramedullary canal is not a major problem, a procedure which avoids such drilling is preferred. Additionally, in conventional procedures for TKA and UKA, the cutting is performed anterior to posterior which may result in cutting or other trauma to the posterior cruciate ligament (PCL) and the anterior cruciate ligament (ACL). A major disadvantage of prior art instrumentation for cutting, in addition to the invasive drilling a hole in the intramedullary canal, is that there is no extra-medullary reference point to assist in making the cut surfaces of the condyles at 90xc2x0 to the rod extending outwardly from the intra-medullary canal.
The present invention is directed to a surgical procedure with a new approach to UKA and DKA and to extramedullary instrumentation for use in performing such procedure which is designed to be minimally invasive. The instrumentation allows the surgeon to align the femoral component without use of an intramedullary guide hole, thus reducing post operative morbidity and allowing more rapid return to normal function. The present invention includes to an orthopedic saw guide assembly and a method for using which permits precise cutting. The saw guide assembly including the related positioning components are located externally of the intramedullary canal. Accordingly, the apparatus may be characterized as an extra-medullary, minimally invasive unicompartmental/dual-compartmental femoral knee saw guide. It permits precise positioning to obtain a cut which is perpendicular to the mechanical axis while also permitting the cut to be made from medial to lateral or lateral to medial directions. Cutting in a medial to lateral or lateral to medial direction eliminates any need to cut the PCL or ACL, avoids the problem of anterior soft tissue impingement and avoids the need to evert or subluxate the patella. In addition to permitting the patient to return to normal function more rapidly than is possible with anterior to posterior or cutting, the present invention greatly reduces surgical time and effort.